MAXIM MAX630, MAX4193 User Manual

General Description

Maxim’s MAX630 and MAX4193 CMOS DC-DC regula­tors are designed for simple, efficient, minimum-size
DC-DC converter circuits in the 5mW to 5W range. The
MAX630 and MAX4193 provide all control and power
handling functions in a compact 8-pin package: a

1.31V bandgap reference, an oscillator, a voltage com­parator, and a 375mA N-channel output MOSFET. A
comparator is also provided for low-battery detection.

Operating current is only 70µA and is nearly indepen­dent of output switch current or duty cycle. A logic-level
input shuts down the regulator to less than 1µA quies­cent current. Low-current operation ensures high effi­ciency even in low-power battery-operated systems.
The MAX630 and MAX4193 are compatible with most
battery voltages, operating from 2.0V to 16.5V.

The devices are pin compatible with the Raytheon bipo­lar circuits, RC4191/2/3, while providing significantly
improved efficiency and low-voltage operation. Maxim
also manufactures the MAX631, MAX632, and MAX633
DC-DC converters, which reduce the external compo­nent count in fixed-output 5V, 12V, and 15V circuits.
See Table 2 at the end of this data sheet for a summary
of other Maxim DC-DC converters.

Applications

+5V to +15V DC-DC Converters
High-Efficiency Battery-Powered DC-DC

Converters
+3V to +5V DC-DC Converters
9V Battery Life Extension
Uninterruptible 5V Power Supplies
5mW to 5W Switch-Mode Power Supplies

Features

♦ High Efficiency—85% (typ)
♦ 70µA Typical Operating Current
♦ 1µA Maximum Quiescent Current
♦ 2.0V to 16.5V Operation
♦ 525mA (Peak) Onboard Drive Capability
♦ ±1.5% Output Voltage Accuracy (MAX630)
♦ Low-Battery Detector
♦ Compact 8-Pin Mini-DIP and SO Packages
♦ Pin Compatible with RC4191/2/3

MAX630/MAX4193

CMOS Micropower Step-Up

Switching Regulator

________________________________________________________________ Maxim Integrated Products 1

I

C

+V

S

GND

1

2

87LBD

V

FB

C

X

L

X

LBR

TOP VIEW

3

4

6

5

MAX630

MAX4193

Pin Configuration

Ordering Information

MAX630

+5V IN

470μH

+15V
OUT

47pF

8

LBD

1

LBR

2

C

X

4

GND

7

V

FB

3

L

X

6

I

C

5

+V

S

+5 TO +15V CONVERTER

Typical Operating Circuit

19-0915; Rev 2; 9/08

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

*Dice are specified at TA= +25°C. Contact factory for dice
specifications.

**Contact factory for availability and processing to MIL-STD-883.
†Contact factory for availibility.

PART TEMP RANGE

MAX630CPA 0°C to +70°C 8 PDIP

MAX630CSA 0°C to +70°C 8 SO
MAX630CJA 0°C to +70°C 8 CERDIP
MAX630EPA -40°C to +85°C 8 PDIP
MAX630ESA -40°C to +85°C 8 SO
MAX630EJA -40°C to +85°C 8 CERDIP
MAX630MJA -55°C to +125°C 8 CERDIP**
MAX630MSA/PR -55°C to +125°C 8 SO†
M AX 630M S A/P R- T -55°C to +125°C 8 SO†
MAX4193C/D 0°C to +70°C Dice*
MAX4193CPA 0°C to +70°C 8 PDIP
MAX4193CSA 0°C to +70°C 8 SO
MAX4193CJA 0°C to +70°C 8 CERDIP
MAX4193EPA -40°C to +85°C 8 PDIP
MAX4193ESA -40°C to +85°C 8 SO
MAX4193EJA -40°C to +85°C 8 CERDIP
MAX4193MJA -55°C to +125°C 8 CERDIP**

PIN­PACKAGE

MAX630/MAX4193

CMOS Micropower Step-Up
Switching Regulator

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(+VS= +6.0V, TA= +25°C, IC= 5.0µA, unless otherwise noted.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

Supply Voltage .......................................................................18V

Storage Temperature Range ............................-65°C to +160°C

Lead Temperature (soldering, 10s) .................................+300°C

Operating Temperature Range

MAX630C, MAX4193C........................................0°C to +70°C

MAX630E, MAX4193E .....................................-40°C to +85°C

MAX630M, MAX4193M..................................-55°C to +125°C

Power Dissipation

8-Pin PDIP (derate 6.25mW/°C above +50°C).............468mW

8-Pin SO (derate 5.88mW/°C above +50°C)................441mW

8-Pin CERDIP (derate 8.33mW/°C above +50°C)........833mW

Input Voltage (Pins 1, 2, 6, 7) .....................-0.3V to (+V

S

+ 0.3V)

Output Voltage, L

X

and LBD ..................................................18V

L

X

Output Current ..................................................525mA (Peak)

LBD Output Current ............................................................50mA

MAX630 MAX4193

PARAMETER

CONDITIONS

UNITS

Operating 2.0

Supply Voltage +V

S

Startup 1.9

2.4

V

Internal Reference Voltage V

REF

V

Switch Current I

SW

V3 = 400mV 75

75

mA

Supply Current (at Pin 5) I

S

I3 = 0mA 70

90 µA

Efficiency 85 85 %

Line Regulation

0.5V

0

< VS < V

0

(Note 1)

0.2

0.5

% V

OUT

Load Regulation

V

S

= +5V, P

LOAD

= 0 to

150mW (Note 1)

0.5 0.2 0.5

% V

OUT

Operating Frequency Range

F

O

(Note 2) 0.1 40 75 0.1 25 75 kHz

Reference Set Internal
Pulldown Resistance

R

IC

V6 = V

S

0.5

10 0.5 1.5 10 MΩ

Reference Set Input Voltage
Threshold

V

IC

0.2

1.3 0.2 0.8 1.3 V

Switch Current I

SW

V3 = 1.0V

mA

Switch Leakage Current I

CO

V3 = 16.5V

1.0

5.0 µA

Supply Current (Shutdown) I

SO

IC < 0.01µA

1.0

5.0 µA

Low-Battery Bias Current I

LBR

10

10 nA

Capacitor Charging Current I

CX

30 30 µA

CX+ Threshold Voltage +VS - 0.1 +VS - 0.1 V

CX- Threshold Voltage

0.1 V

VFB Input Bias Current I

FB

10

10 nA

Low-Battery Detector Output
Current

I

LBD

V8 = 0.4V, V1 = 1.1V

µA

Low-Battery Detector Output
Leakage

I

LBDO

V8 = 16.5V, V1 = 1.4V

5.0

5.0 µA

SYMBOL

MIN TYP MAX MIN TYP MAX

1.29 1.31 1.33 1.24 1.31 1.38

150

16.5

150

125

16.5

100 100

250 600 250 600

0.08

0.2

1.5

0.8

0.01

0.01

0.01

0.1

0.01

0.01

0.06

0.01

0.01

0.01

0.01

0.01

MAX630/MAX4193

CMOS Micropower Step-Up

Switching Regulator

_______________________________________________________________________________________ 3

LX ON-RESISTANCE vs.

TEMPERATURE

MAX630/4193 toc01

TEMPERATURE (°C)

L

X

R

ON

(Ω)

1007550250-25-50

2

4

6

8

0

125

+VS = 2.5V

+VS = 6V

+VS = 16V

SUPPLY CURRENT vs.

TEMPERATURE

MAX630/4193 toc02

TEMPERATURE (°C)

I

S

(μA)

1007550250-25-50

40

20

80

60

120

100

140

0

125

SUPPLY CURRENT vs.

SUPPLY VOLTAGE

MAX630/4193 toc03

+VS (V)

I

S

(μA)

1412108642

50

150

100

250

200

300

16

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

ELECTRICAL CHARACTERISTICS

(+VS= +6.0V, TA= Full Operating Temperature Range, IC= 5.0µA, unless otherwise noted.)

MAX630 MAX4193

PARAMETER

CONDITIONS

UNITS

Supply Voltage +V

S

V

Internal Reference Voltage V

REF

V

Supply Current (Pin 5) I

S

I3 = 0mA 70

90

µA

Line Regulation

0.5V

0UT

< VS < V

0UT

(Note 1)

0.5

1.0

% V

OUT

Load Regulation

V

S

= 0.5V0, PL = 0 to

150mW (Note 1)

1.0

1.0

% V

OUT

0°C ≤ TA ≤
+70°C

10

10

-40°C ≤ TA ≤
+85°C

10

10

Reference Set Internal
Pulldown Resistance

R

IC

-55°C ≤ TA ≤
+125°C

10

10

MΩ

Reference Set Input Voltage
Threshold

V

IC

1.3

1.3 V

Switch Leakage Current I

CO

V3 = 16.5V

30

30 µA

Supply Current (Shutdown) I

SO

IC < 0.01µA

10

30 µA

Low-Battery Detector Output
Current

I

LBD

V8 = 0.4V, V1 = 1.1V

µA

Note 1: Guaranteed by correlation with DC pulse measurements.
Note 2: The operating frequency range is guaranteed by design and verified with sample testing.

SYMBOL

V6 = V

S

MIN TYP MAX MIN TYP MAX

2.2 16.5 3.5 16.5

1.25 1.31 1.37 1.20 1.31 1.42

0.2

0.5

0.45 1.5

0.4 1.5

0.3 1.5

0.2 0.8

0.1

0.01

250 600 250 600

200

300

0.5

0.5

0.45 1.5

0.4 1.5

0.3 1.5

0.2 0.8

0.1

0.01

Detailed Description

The operation of the MAX630 can best be understood
by examining the voltage regulating loop of Figure 1.
R1 and R2 divide the output voltage, which is com­pared with the 1.3V internal reference by comparator
COMP1. When the output voltage is lower than desired,
the comparator output goes high and the oscillator out­put pulses are passed through the NOR gate latch,
turning on the output N-channel MOSFET at pin 3, LX.
As long as the output voltage is less than the desired
voltage, pin 3 drives the inductor with a series of pulses
at the oscillator frequency.

Each time the output N-channel MOSFET is turned on,
the current through the external coil, L1, increases,
storing energy in the coil. Each time the output turns off,
the voltage across the coil reverses sign and the volt­age at LXrises until the catch diode, D1, is forward
biased, delivering power to the output.

When the output voltage reaches the desired level,

1.31V x (1 + R1 / R2), the comparator output goes low
and the inductor is no longer pulsed. Current is then
supplied by the filter capacitor, C1, until the output volt­age drops below the threshold, and once again LXis
switched on, repeating the cycle. The average duty
cycle at LXis directly proportional to the output current.

Output Driver (LX Pin)

The MAX630/MAX4193 output device is a large
N-channel MOSFET with an on-resistance of 4Ω and a
peak current rating of 525mA. One well-known advan­tage that MOSFETs have over bipolar transistors in
switching applications is higher speed, which reduces
switching losses and allows the use of smaller, lighter,
less costly magnetic components. Also important is that
MOSFETs, unlike bipolar transistors, do not require
base current that, in low-power DC-DC converters,
often accounts for a major portion of input power.

The operating current of the MAX630 and MAX4193
increases by approximately 1µA/kHz at maximum
power output due to the charging current required by
the gate capacitance of the LXoutput driver (e.g., 40µA
increase at a 40kHz operating frequency). In compari­son, equivalent bipolar circuits typically drive their NPN
LXoutput device with 2mA of base drive, causing the
bipolar circuit’s operating current to increase by a fac­tor of 10 between no load and full load.

Oscillator

The oscillator frequency is set by a single external, low­cost ceramic capacitor connected to pin 2, CX. 47pF
sets the oscillator to 40kHz, a reasonable compromise
between lower switching losses at low frequencies and
reduced inductor size at higher frequencies.

MAX630/MAX4193

CMOS Micropower Step-Up
Switching Regulator

4 _______________________________________________________________________________________

Pin Description

PIN NAME FUNCTION

1 LBR

Low-Battery Detection Comparator Input. The LBD output, pin 8, sinks current whenever this pin is
below the low-battery detector threshold, typically 1.31V.

2C

X

An external capacitor connected between this terminal and ground sets the oscillator frequency.
47pF = 40 kHz.

3L

X

This pin drives the external inductor. The internal N-channel MOSFET that drives LX has an output
resistance of 4Ω and a peak current rating of 525mA.

4 GND Ground

5+VSThe positive supply voltage, from 2.0V to 16.5V (MAX630).

6I

C

The MAX630/MAX4193 shut down when this pin is left floating or is driven below 0.2V. For normal
operation, connect I

C

directly to +VS or drive it high with either a CMOS gate or pullup resistor

connected to +V

S

. The supply current is typically 10nA in the shutdown mode

7V

FB

The output voltage is set by an external resistive divider connected from the converter output to V

FB

and ground. The MAX630/MAX4193 pulse the LX output whenever the voltage at this terminal is less
than 1.31V.

8 LBD

The Low-Battery Detector output is an open-drain N-channel MOSFET that sinks up to 600μA (typ)
whenever the LBR input, pin 1, is below 1.31V.

Low-Battery Detector

The low-battery detector compares the voltage on LBR
with the internal 1.31V reference. The output, LBD, is an
open-drain N-channel MOSFET. In addition to detecting
and warning of a low battery voltage, the comparator
can also perform other voltage-monitoring operations
such as power-failure detection.

Another use of the low-battery detector is to lower the
oscillator frequency when the input voltage goes below
a specified level. Lowering the oscillator frequency
increases the available output power, compensating for
the decrease in available power caused by reduced
input voltage (see Figure 5).

Logic-Level Shutdown Input

The shutdown mode is entered whenever IC(pin 6) is
driven below 0.2V or left floating. When shut down, the

MAX630’s analog circuitry, oscillator, LX, and LBD out­puts are turned off. The device’s quiescent current dur­ing shutdown is typically 10nA (1µA max).

Bootstrapped Operation

In most circuits, the preferred source of +VSvoltage for
the MAX630 and MAX4193 is the boosted output volt­age. This is often referred to as a “bootstrapped” oper­ation since the circuit figuratively “lifts” itself up.

The on-resistance of the N-channel LX output decreas­es with an increase in +VS; however, the device operat­ing current goes up with +VS(see the Typical
Operating Characteristics, ISvs. +VSgraph). In circuits
with very low output current and input voltages greater
than 3V, it may be more efficient to connect +VSdirect­ly to the input voltage rather than bootstrap.

MAX630/MAX4193

CMOS Micropower Step-Up

Switching Regulator

_______________________________________________________________________________________ 5

COMP 2

+5V INPUT

R3

169kΩ

R4
100kΩ

L1
470

LOW BATTERY INPUT

1.31V

OSC

RON ≅ 3Ω

40kHz

COMP 1

1.31V

BANDGAP

REFERENCE

AND

BIAS GENERATOR

1 LBR

2C

X

3L

X

4 GND

D1
1N4148

+VS5

I

C

6

V

FB

7

LBD 8

LOW-BATTERY OUTPUT
(LOW IF INPUT < 3V)

C

C

R1
499kΩ

R2

47.5kΩ

SHUTDOWN

OPERATE

+15V OUTPUT
20mA

C1
470μF
25V

MAX630

COMP 2

Figure 1. +5V to +15V Converter and Block Diagram

MAX630/MAX4193

External Components

Resistors

Since the LBR and VFBinput bias currents are specified
as 10nA (max), the current in the dividers R1/R2 and
R3/R4 (Figure 1) may be as low as 1µA without signifi­cantly affecting accuracy. Normally R2 and R4 are
between 10kΩ and 1MΩ, which sets the current in the
voltage-dividers in the 1.3µA to 130µA range. R1 and
R3 can then be calculated as follows:

where V

OUT

is the desired output voltage and VLBis

the desired low-battery warning threshold.

If the IC(shutdown) input is pulled up through a resistor
rather than connected directly to +VS, the current
through the pullup resistor should be a minimum of 4µA
with ICat the input-high threshold of 1.3V:

Inductor Value

The available output current from a DC-DC voltage
boost converter is a function of the input voltage, exter­nal inductor value, output voltage, and the operating
frequency.

The inductor must 1) have the correct inductance, 2) be
able to handle the required peak currents, and 3) have
acceptable series resistance and core losses. If the
inductance is too high, the MAX630 will not be able to
deliver the desired output power, even with the LXout­put on for every oscillator cycle. The available output
power can be increased by either decreasing the
inductance or the frequency. Reducing the frequency
increases the on-period of the LXoutput, thereby
increasing the peak inductor current. The available out­put power is increased since it is proportional to the
square of the peak inductor current (IPK).

where P

OUT

includes the power dissipated in the catch

diode (D1) as well as that in the load. If the inductance
is too low, the current at LXmay exceed the maximum
rating. The minimum allowed inductor value is
expressed by:

where I

MAX

≈ 525mA (peak LXcurrent) and tONis the

on-time of the LXoutput.

The most common MAX630 circuit is a boost-mode
converter (Figure 1). When the N-channel output device
is on, the current linearly rises since:

At the end of the on-time (14µs for 40kHz, 55% duty­cycle oscillator) the current is:

The energy in the coil is:

At maximum load, this cycle is repeated 40,000 times
per second, and the power transferred through the coil
is 40,000 x 5.25 = 210mW. Since the coil only supplies
the voltage above the input voltage, at 15V, the DC-DC
converter can supply 210mW / (15V - 5V) = 21mA. The
coil provides 210mW and the battery directly supplies
another 105mW, for a total of 315mW of output power. If
the load draws less than 21mA, the MAX630 turns on its
output only often enough to keep the output voltage at
a constant 15V.

Reducing the inductor value increases the available
output current: lower L increases the peak current,
thereby increasing the available power. The external
inductor required by the MAX630 is readily obtained
from a variety of suppliers (Table 1). Standard coils are
suitable for most applications.

Types of Inductors

Molded Inductors

These are cylindrically wound coils that look similar to
1W resistors. They have the advantages of low cost and
ease of handling, but have higher resistance, higher
losses, and lower power handling capability than other
types.

ImA

pk

VT

L

Vx s

H

ON

==

μ

μ

=

514

470

150

didtV

L

=

L

MIN

VT

I

IN ON

MAX

=

L

VT f

P

ce P

LI f

and I

IN ON

OUT

OUT

pk

pk

VT

L

IN ON

=

=

=

()

sin :

:

2

2

2

2

R

VV

A

IC

S

≤

+−μ134.

10 2 1 1 2

131

131

10 4 1 3 4

131

131

ΩΩ

ΩΩ

≤≤ =

−

≤≤ =

−

.

.

.

.

RMRRx

VV

RMRRx

VV

OUT

LB

CMOS Micropower Step-Up
Switching Regulator

6 _______________________________________________________________________________________

EJ

LI

pk

=

=μ

2

2

525.

Potted Toroidal Inductors

A typical 1mH, 0.82Ω potted toroidal inductor (Dale TE­3Q4TA) is 0.685in in diameter by 0.385in high and
mounts directly onto a PC board by its leads. Such
devices offer high efficiency and mounting ease, but at
a somewhat higher cost than molded inductors.

Ferrite Cores (Pot Cores)

Pot cores are very popular as switch-mode inductors
since they offer high performance and ease of design.
The coils are generally wound on a plastic bobbin,
which is then placed between two pot core sections. A
simple clip to hold the core sections together com­pletes the inductor. Smaller pot cores mount directly
onto PC boards through the bobbin terminals. Cores
come in a wide variety of sizes, often with the center
posts ground down to provide an air gap. The gap pre­vents saturation while accurately defining the induc­tance per turn squared.

Pot cores are suitable for all DC-DC converters, but are
usually used in the higher power applications. They are
also useful for experimentation since it is easy to wind
coils onto the plastic bobbins.

Toroidal Cores

In volume production, the toroidal core offers high per­formance, low size and weight, and low cost. They are,
however, slightly more difficult for prototyping, in that
manually winding turns onto a toroid is more tedious
than on the plastic bobbins used with pot cores.

Toroids are more efficient for a given size since the flux
is more evenly distributed than in a pot core, where the
effective core area differs between the post, side, top,
and bottom.

Since it is difficult to gap a toroid, manufacturers produce
toroids using a mixture of ferromagnetic powder (typically
iron or Mo-Permalloy powder) and a binder. The perme­ability is controlled by varying the amount of binder,
which changes the effective gap between the ferromag­netic particles. Mo-Permalloy powder (MPP) cores have
lower losses and are recommended for the highest effi­ciency, while iron powder cores are lower cost.

Diodes

In most MAX630 circuits, the inductor current returns to
zero before LXturns on for the next output pulse. This
allows the use of slow turn-off diodes. On the other
hand, the diode current abruptly goes from zero to full
peak current each time L

X

switches off (Figure 1, D1).
To avoid excessive losses, the diode must therefore
have a fast turn-on time.

For low-power circuits with peak currents less than
100mA, signal diodes such as 1N4148s perform well.
For higher-current circuits, or for maximum efficiency at
low power, the 1N5817 series of Schottky diodes are
recommended. Although 1N4001s and other general­purpose rectifiers are rated for high currents, they are
unacceptable because their slow turn-on time results in
excessive losses.

MAX630/MAX4193

CMOS Micropower Step-Up

Switching Regulator

_______________________________________________________________________________________ 7

MANUFACTURER TYPICAL PART NUMBER DESCRIPTION

MOLDED INDUCTORS

Dale IHA-104 500µH, 0.5Ω

Nytronics WEE-470 470µH, 10Ω

TRW LL-500 500µH, 0.75Ω

POTTED TOROIDAL INDUCTORS

Dale TE-3Q4TA 1mH, 0.82Ω

TRW MH-1 600µH, 1.9Ω

Torotel Prod. PT 53-18 500µH, 5Ω

FERRITE CORES AND TOROIDS

Allen Bradley T0451S100A Tor. core, 500nH/T

2

Siemens B64290-K38-X38 Tor. core, 4µH/T

2

Magnetics 555130 Tor. core, 53nH/T

2

Stackpole 57-3215 Pot core, 14mm x 18mm

Magnetics G-41408-25 Pot core, 14 x 8, 250nH/T

2

Table 1. Coil and Core Manufacturers

Note: This list does not constitute an endorsement by Maxim Integrated Products and is not intended to be a comprehensive list of

all manufacturers of these components.

MAX630/MAX4193

Filter Capacitor

The output-voltage ripple has two components, with
approximately 90 degrees phase difference between
them. One component is created by the change in the
capacitor’s stored charge with each output pulse. The
other ripple component is the product of the capacitor’s
charge/discharge current and its effective series resis­tance (ESR). With low-cost aluminum electrolytic
capacitors, the ESR-produced ripple is generally larger
than that caused by the change in charge.

where VINis the coil input voltage, L is its inductance, f
is the oscillator frequency, and ESR is the equivalent
series resistance of the filter capacitor.

The output ripple resulting from the change in charge
on the filter capacitor is:

where t

CHG

and t

DIS

are the charge and discharge
times for the inductor (1/2f can be used for nominal cal­culations).

Oscillator Capacitor, C

X

The oscillator capacitor, CX, is a noncritical ceramic or
silver mica capacitor. CXcan also be calculated by:

where f is the desired operating frequency in Hertz, and
C

INT

is the sum of the stray capacitance on the CXpin
and the internal capacitance of the package. The internal
capacitance is typically 1pF for the plastic package and
3pF for the CERDIP package. Typical stray capacitances
are about 3pF for normal PC board layouts, but will be
significantly higher if a socket is used.

Bypassing and Compensation

Since the inductor-charging current can be relatively
large, high currents can flow through the ground con­nection of the MAX630/MAX4193. To prevent unwanted
feedback, the impedance of the ground path must be
as low as possible, and supply bypassing should be
used for the device.

When large values (>50kΩ) are used for the voltage­setting resistors, R1 and R2 of Figure 1, stray capaci­tance at the VFBinput can add a lag to the feedback
response, destabilizing the regulator, increasing low­frequency ripple, and lowering efficiency. This can
often be avoided by minimizing the stray capacitance
at the VFBnode. It can also be remedied by adding a
lead compensation capacitor of 100pF to 10nF in paral­lel with R1 in Figure 1.

DC-DC Converter Configurations

DC-DC converters come in three basic topologies:
buck, boost, and buck-boost (Figure 2). The MAX630 is
usually operated in the positive-voltage boost circuit,
where the output voltage is greater than the input.

The boost circuit is used where the input voltage is
always less than the desired output and the buck circuit
is used where the input is greater than the output. The
buck-boost circuit inverts, and can be used with, input

C

X

f

C C pF see text

X INT INT

=−

−
≅

214 10

5

6

.

(,)

V

Q
C

where Q t x

I

and I t x

V

L

V

Vt t

LC

dQ DIS

PEAK

PEAK CHG

IN

dQ

IN CHG DIS

==

=

=

,

,

()()

2

2

V I x ESR

V

Lf

xESR Voltsp p

ESR PK

IN

==

⎛
⎝

⎜

⎞
⎠

⎟

−

2

()

CMOS Micropower Step-Up
Switching Regulator

8 _______________________________________________________________________________________

CONTROL

SECTION

V

BATT

S

1

V

OUT

> V

BATT

+

-

BOOST CONVERTER

CONTROL

SECTION

V

BATT

S

1

V

OUT

< V

BATT

+

-

BUCK CONVERTER

CONTROL

SECTION

V

BATT

S

1

|V

OUT

| < OR > V

BATT

+

-

BUCK-BOOST CONVERTER

Figure 2. DC-DC Converter Configurations

voltages that are either greater or less than the output.

DC-DC converters can also be classified by the control
method. The two most common are pulse-width modu­lation (PWM) and pulse-frequency modulation (PFM).
PWM switch-mode power-supply ICs (of which current­mode control is one variant) are well-established in
high-power off-line switchers. Both PWM and PFM cir­cuits control the output voltage by varying duty cycle.
In the PWM circuit, the frequency is held constant and
the width of each pulse is varied. In the PFM circuit, the
pulse width is held constant and duty cycle is con­trolled by changing the pulse repetition rate.

The MAX630 refines the basic PFM by employing a con­stant-frequency oscillator. Its output MOSFET is switched
on when the oscillator is high and the output voltages is
lower than desired. If the output voltage is higher than
desired, the MOSFET output is disabled for that oscillator
cycle. This pulse skipping varies the average duty cycle,
and thereby controls the output voltage.

Note that, unlike the PWM ICs, which use an op amp as
the control element, the MAX630 uses a comparator to
compare the output voltage to an onboard reference.
This reduces the number of external components and
operating current.

Typical Applications

+5V to +15V DC-DC Converter

Figure 1 shows a simple circuit that generates +15V at
approximately 20mA from a +5V input. The MAX630
has a ±1.5% reference accuracy, so the output voltage
has an untrimmed accuracy of ±3.5% if R1 and R2 are
1% resistors. Other output voltages can also be select­ed by changing the feedback resistors. Capacitor C

X

sets the oscillator frequency (47pF = 40kHz), while C1
limits output ripple to about 50mV.

With a low-cost molded inductor, the circuit’s efficiency
is about 75%, but an inductor with lower series resis­tance such as the Dale TE3Q4TA increases efficiency
to around 85%. A key to high efficiency is that the
MAX630 itself is powered from the +15V output. This
provides the onboard N-channel output device with 15V
gate drive, lowering its on-resistance to about 4Ω.
When +5V power is first applied, current flows through
L1 and D1, supplying the MAX630 with 4.4V for startup.

+5V to ±15V DC-DC Converter

The circuit in Figure 3 is similar to that of Figure 1
except that two more windings are added to the induc­tor. The 1408 (14mm x 8mm) pot core specified is an
IEC standard size available from many manufacturers
(see Table 1). The -15V output is semiregulated, typi-

cally varying from -13.6V to -14.4V as the +15V load
current changes from no load to 20mA.

2.5W, 3V to 5V DC-DC Converter

Some systems, although battery powered, need high
currents for short periods, and then shut down to a low­power state. The extra circuitry of Figure 4 is designed to
meet these high-current needs. Operating in the buck­boost or flyback mode, the circuit converts -3V to +5V.
The left side of Figure 4 is similar to Figure 1 and sup­plies 15V for the gate drive of the external power MOS­FET. This 15V gate drive ensures that the external device
is completely turned on and has low on-resistance.

The right side of Figure 4 is a -3V to +5V buck-boost
converter. This circuit has the advantage that when the
MAX630 is turned off, the output voltage falls to 0V,
unlike the standard boost circuit, where the output volt­age is V

BATT

- 0.6V when the converter is shut down.
When shut down, this circuit uses less than 10µA, with
most of the current being the leakage current of the
power MOSFET.

The inductor and output-filter capacitor values have
been selected to accommodate the increased power
levels. With the values indicated, this circuit can supply
up to 500mA at 5V, with 85% efficiency. Since the left
side of the circuit powers only the right-hand MAX630,
the circuit starts up with battery voltages as low as

1.5V, independent of the loading on the +5V output.

MAX630/MAX4193

CMOS Micropower Step-Up

Switching Regulator

_______________________________________________________________________________________ 9

MAX630

1MΩ

95.3kΩ

47pF

7

V

FB

2

C

X

GND LBD

N.C.

GND

1

L

X

3

65

48

I

C

+V

S

+5V

330μF
25V

330μF
25V

1:3:3
220μH PRIMARY
14 x 8mm POT CORE

ALL DIODES IN4148

Figure 3. +5V to ±15V Converter

MAX630/MAX4193

+3V Battery to +5V DC-DC Converter

A common power-supply requirement involves conver­sion of a 2.4V or 3V battery voltage to a 5V logic sup­ply. The circuit in Figure 5 converts 3V to 5V at 40mA
with 85% efficiency. When IC(pin 6) is driven low, the
output voltage will be the battery voltage minus the
drop across diode D1.

The optional circuitry using C1, R3, and R4 lowers the
oscillator frequency when the battery voltage falls to

2.0V. This lower frequency maintains the output-power
capability of the circuit by increasing the peak inductor
current, compensating for the reduced battery voltage.

Uninterruptable +5V Supply

In Figure 6, the MAX630 provides a continuous supply
of regulated +5V, with automatic switchover between
line power and battery backup. When the line-powered
input voltage is at +5V, it provides 4.4V to the MAX630
and trickle charges the battery. If the line-powered
input falls below the battery voltage, the 3.6V battery
supplies power to the MAX630, which boosts the bat­tery voltage up to +5V, thus maintaining a continuous
supply to the uninterruptable +5V bus. Since the +5V
output is always supplied through the MAX630, there
are no power spikes or glitches during power transfer.

The MAX630’s low-battery detector monitors the line­powered +5V, and the LBD output can be used to shut
down unnecessary sections of the system during power
failures. Alternatively, the low-battery detector could
monitor the NiCad battery voltage and provide warning
of power loss when the battery is nearly discharged.

Unlike battery backup systems that use 9V batteries,
this circuit does not need +12V or +15V to recharge the
battery. Consequently, it can be used to provide +5V
backup on modules or circuit cards that only have 5V
available.

9V Battery Life Extender

Figure 7’s circuit provides a minimum of 7V until the 9V
battery voltage falls to less than 2V. When the battery
voltage is above 7V, the MAX630’s ICpin is low, putting
it into the shutdown mode that draws only 10nA. When
the battery voltage falls to 7V, the MAX8212 voltage
detector’s output goes high, enabling the MAX630. The
MAX630 then maintains the output voltage at 7V, even
as the battery voltage falls below 7V. The LBD is used
to decrease the oscillator frequency when the battery
voltage falls to 3V, thereby increasing the output cur­rent capability of the circuit.

CMOS Micropower Step-Up
Switching Regulator

10 ______________________________________________________________________________________

MAX630

47μF

25V

2mH

3

L

X

2

C

X

57

+V

S

47pF

1N4148
SHUTDOWN

6

4

I

C

GND

3V

LITHIUM

CELL

OPERATE

V

FB

499kΩ

47.6kΩ

SECTION 1 SECTION 2

+12V

MAX630

3

L

X

2

C

X

7

5

4

+V

S

6

I

C

GND

V

FB

47pF

10kΩ

280kΩ

100kΩ

1/6 4069

33μH

IRF543

1N5817

470μF

+5V AT 0.5A

Figure 4. High-Power 3V to 5V Converter with Shutdown

Note that this circuit (with or without the MAX8212) can be
used to provide 5V from four alkaline cells. The initial volt­age is approximately 6V, and the output is maintained at
5V even when the battery voltage falls to less than 2V.

Dual-Tracking Regulator

A MAX634 inverting regulator is combined with a
MAX630 in Figure 8 to provide a dual-tracking ±15V

output from a 9V battery. The reference for the -15V
output is derived from the positive output through R3
and R4. Both regulators are set to maximize output
power at low-battery voltage by reducing the oscillator
frequency, through LBR, when V

BATT

falls to 7.2V.

MAX630/MAX4193

CMOS Micropower Step-Up

Switching Regulator

______________________________________________________________________________________ 11

MAX630

3V

R3
249kΩ

R4
499kΩ

R

1

540kΩ

R

2

200kΩ

C1

100pF

C

X

47pF

LBD8C

X

GND

2

L

X

4

1

LBR

LX 470μH

1N4148

+5V OUT

470μF
15V

3

5

+V

S

7

V

FB

6

I

C

Figure 5. 3V to 5V Converter with Low-Battery Frequency Shift

MAX8212

MAX630

10MΩ

HYST

OUT

2

THRESHOLD

3

GND

5

82.4MΩ

390kΩ

9V

BATTERY

1.3MΩ

1MΩ

1

LBR

2MΩ

560kΩ

7

6

I

C

V

FB

47pF

100pF

LBD

8

C

X

L

X

2

3

GND

4

1MΩ

+V

S

5

1.0mH

470μF
25V

Figure 7. Battery Life Extension Down to 3V In

MAX630

LINE-POWERED

+5V INPUT

1N4001

200kΩ

100kΩ

680Ω

1N5817

3.6V

NICAD

BATTERY

470μH

1

LBR

8

LBD

GND

4

C

X

L

X

2

3

280kΩ

100kΩ

1N5817

UNINTERRUPTABLE

+5V OUTPUT

470μF
15V

5

+V

S

7

V

FB

6

I

C

POWER FAIL

47pF

Figure 6. Uninterruptable +5V Supply

MAX630/MAX4193

CMOS Micropower Step-Up
Switching Regulator

12 ______________________________________________________________________________________

Table 2. Maxim DC-DC Converters

MAX634 MAX630

150μF

NEG OUT

-12V, 15mA

250μH

1N914

R3

100kΩ

R4

100kΩ

5

L

X

8

V

FB

7

V

REF

6

+V

S

N.C.

GND

4

C

X

3

LBD

2

150pF

68pF

C

X

+V

S

2

LBD8LBR

1

100pF

47pF

4

GND

6

I

C

R6
18kΩ

R5
100kΩ

5

L

X

3

500μH

7

V

FB

IN914

R1
82kΩ

R2
10kΩ

330μF

INPUT, 9V BATTERY

POS OUT
+12V, 45mA

Figure 8. ±12V Dual-Tracking Regulator

DEVICE DESCRIPTION INPUT VOLTAGE OUTPUT VOLTAGE COMMENTS

ICL7660 Charge-Pump Voltage Inverter 1.5V to 10V -V

MAX4193 DC-DC Boost Converter 2.4V to 16.5V V

MAX630 DC-DC Boost Converter 2.0V to 16.5V V

OUT

OUT

IN

> V

> V

IN

IN

MAX631 DC-DC Boost Converter 1.5V to 5.6V +5V Only 2 external components

MAX632 DC-DC Boost Converter 1.5V to 12.6V +12V Only 2 external components

MAX633 DC-DC Boost Converter 1.5V to 15.6V +15V Only 2 external components

MAX4391 DC-DC Voltage Inverter 4V to 16.5V Up to -20V RC4391 2nd source

MAX634 DC-DC Voltage Inverter 2.3V to 16.5V Up to -20V Improved RC4391 2nd source

MAX635 DC-DC Voltage Inverter 2.3V to 16.5V -5V Only 3 external components

MAX636 DC-DC Voltage Inverter 2.3V to 16.5V -12V Only 3 external components

MAX637 DC-DC Voltage Inverter 2.3V to 16.5V -15V Only 3 external components

MAX638 DC-DC Voltage Step-Down 3V to 16.5V V

MAX641 High-Power Boost Converter 1.5V to 5.6V +5V Drives external MOSFET

MAX642 High-Power Boost Converter 1.5V to 12.6V +12V Drives external MOSFET

MAX643 High-Power Boost Converter 1.5V to 15.6V +15V Drives external MOSFET

OUT

< V

IN

Not regulated

RC4193 2nd source

Improved RC4191 2nd source

Only 3 external components

MAX630/MAX4193

CMOS Micropower Step-Up

Switching Regulator

______________________________________________________________________________________ 13

Package Information

For the latest package outline information, go to

www.maxim-ic.com/packages

.

Chip Topography

LBR

1

7

I

C

V

FB

6

2

GND

3

4

GND

4

+V

S

5

0.070"

(1.78mm)

0.089"

(2.26mm)

C

X

L

X

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

8 PDIP P8-T 21-0043

8 SO S8-4 21-0041

8 CERDIP J8-2 21-0045

MAX630/MAX4193

CMOS Micropower Step-Up
Switching Regulator

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

Revision History

REVISION

NUMBER

REVISION

DATE

DESCRIPTION

PAGES

CHANGED

2 9/08 Added information for rugged plastic product 1